<%@ page contentType="image/jpeg" import="java.util.*,java.awt.*,java.io.*,java.awt.image.*,javax.imageio.*" pageEncoding="utf-8"%>    
<%!    
Color getRandColor(int fc,int bc){//给定范围获得随机颜色    
Random random = new Random();    
if(fc>255) fc=255;    
if(bc>255) bc=255;    
int r=fc+random.nextInt(bc-fc);    
int g=fc+random.nextInt(bc-fc);    
int b=fc+random.nextInt(bc-fc);    
return new Color(r,g,b);    
}    
%>    
<%    
//设置页面不缓存    
response.setHeader("Pragma","No-cache");    
response.setHeader("Cache-Control","no-cache");    
response.setDateHeader("Expires", 0);    
   
// 在内存中创建图象    
int width=60, height=20;    
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    
   
// 获取图形上下文    
Graphics g = image.getGraphics();    
   
//生成随机类    
Random random = new Random();    
   
// 设定背景色    
g.setColor(getRandColor(200,250));    
g.fillRect(0, 0, width, height);    
   
//设定字体    
g.setFont(new Font("Times New Roman",Font.PLAIN,18));    
   
//画边框    
//g.setColor(new Color());    
//g.drawRect(0,0,width-1,height-1);    
   
// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到    
g.setColor(getRandColor(160,200));    
for (int i=0;i<155;i++)    
{    
int x = random.nextInt(width);    
int y = random.nextInt(height);    
int xl = random.nextInt(12);    
int yl = random.nextInt(12);    
g.drawLine(x,y,x+xl,y+yl);    
}    
   
// 取随机产生的认证码(4位数字)    
String sRand="";    
for (int i=0;i<4;i++){    
String rand=String.valueOf(random.nextInt(10));    
sRand+=rand;    
// 将认证码显示到图象中    
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成    
g.drawString(rand,13*i+6,16);    
}    
   
// 将认证码存入SESSION    
session.setAttribute("rand",sRand);    
   
// 图象生效    
g.dispose();    
OutputStream output=response.getOutputStream();    
   
// 输出图象到页面    
ImageIO.write(image, "JPEG", response.getOutputStream());    
output.flush();    
out.clear();    
out = pageContext.pushBody();    
   
%>   
